Loudspeaker diaphragm state estimation method and loudspeaker driving circuit using the same

ABSTRACT

A loudspeaker diaphragm state estimation method includes: adjusting a weight value of a diaphragm displacement model by adaptive filtering until an error between an estimated value of a driving voltage of a loudspeaker and a measured value of the driving voltage is less than a predetermined threshold; estimating a diaphragm relative displacement of the loudspeaker according to the diaphragm displacement model corresponding to a final determined weight value; determining a diaphragm relative speed at a next moment based on an input current, a product value of a vector determined by an estimated value of a diaphragm relative speed and an estimated value of a diaphragm relative displacement, and a weight value vector obtained at a present moment; and determining an estimated value of the driving voltage using the estimated value of the diaphragm relative speed, the input current, and a DC impedance of the loudspeaker at the present moment.

RELATED APPLICATIONS

This application claims the benefit of Chinese Patent Application No.201611033206.X, filed on Nov. 17, 2016, which is incorporated herein byreference in its entirety.

FIELD OF THE INVENTION

The present disclosure generally relates to the field of acoustics, andmore particularly to loudspeaker diaphragm state estimation methods andloudspeaker driving circuitry.

BACKGROUND

Loudspeakers can produce sound by driving diaphragms to vibrate throughan electromagnetic field that is generated by an electromagnetic coil.The rated power of a loudspeaker may be limited by its maximum diaphragmoffset value. If the diaphragm offset value exceeds its maximum safetyoffset value, this can cause irreversible damage to the loudspeaker. Insome cases, the output power of the loudspeaker can be made to begreater than the rated power, and the diaphragm offset may be made to beless than the maximum safety offset value. In this way, utilization ofthe loudspeaker can be improved due to the sound possibly being louderthan with the rated power of the loudspeaker.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram of an example loudspeaker diaphragm stateestimation method, in accordance with embodiments of the presentinvention.

FIG. 2 is a schematic block diagram of an example data stream of aloudspeaker diaphragm state estimation method, in accordance withembodiments of the present invention.

FIG. 3 is a diagram of an example electromagnetic and mechanicalvibration model of a loudspeaker, in accordance with embodiments of thepresent invention.

FIG. 4 is a flow diagram of an example method of adjusting a weightvalue, in accordance with embodiments of the present invention.

DETAILED DESCRIPTION

Reference may now be made in detail to particular embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. While the invention may be described in conjunction with thepreferred embodiments, it may be understood that they are not intendedto limit the invention to these embodiments. On the contrary, theinvention is intended to cover alternatives, modifications andequivalents that may be included within the spirit and scope of theinvention as defined by the appended claims. Furthermore, in thefollowing detailed description of the present invention, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present invention. However, it may be readilyapparent to one skilled in the art that the present invention may bepracticed without these specific details. In other instances, well-knownmethods, procedures, processes, components, structures, and circuitshave not been described in detail so as not to unnecessarily obscureaspects of the present invention.

In some portable devices, the requirement on the size of the loudspeakermay be relatively high, and the rated power of the loudspeaker can belimited. Thus, the maximum sound pressure may also be limited. Inparticular embodiments, the loudspeaker diaphragm can operate within asafety operation range, while also increasing its output power and soundpressure, as compared to conventional approaches. Along these lines, thediaphragm displacement of the loudspeaker can be accurately estimated(e.g., by detecting the displacement with laser, detecting the speedwith a laser, detecting the sound pressure, etc.). However, sensors maybe required in one or more of these approaches, and as a result theloudspeaker may be bulky, difficult to install, difficult to implement,and relatively costly, to name a few possible concerns. As such, suchapproaches may not be suitable for practical products.

In one embodiment, a loudspeaker diaphragm state estimation method caninclude: (i) adjusting a weight value of a diaphragm displacement modelby adaptive filtering until an error between an estimated value of adriving voltage of a loudspeaker and a measured value of the drivingvoltage is less than a predetermined threshold; (ii) estimating adiaphragm relative displacement of the loudspeaker according to thediaphragm displacement model that corresponds to a final determinedweight value; (iii) determining a diaphragm relative speed at a nextmoment based on an input current, a product value of a vector determinedby an estimated value of a diaphragm relative speed and an estimatedvalue of a diaphragm relative displacement, and a weight value vectorobtained at a present moment; and (iv) determining an estimated value ofthe driving voltage based on the estimated value of the diaphragmrelative speed, the input current, and a DC impedance of the loudspeakerobtained at the present moment.

Referring now to FIG. 1, which shows a flow diagram of an exampleloudspeaker diaphragm state estimation method, and also to FIG. 2, whichshows a schematic block diagram of an example data stream of aloudspeaker diaphragm state estimation method, in accordance withembodiments of the present invention. At S100, a weight value of adiaphragm displacement model can be adjusted through an adaptivefiltering method, until an error between an estimated value of a drivingvoltage and a measured value of the driving voltage of a loudspeaker isless than a predetermined threshold.

For example, the diaphragm displacement model can calculate or determinea diaphragm relative speed at a next moment based on an input current, aproduct value of a vector determined by an estimated value of adiaphragm relative speed, and an estimated value of a diaphragm relativedisplacement and a weight value vector obtained at a present moment. Inaddition, an estimated value of the driving voltage of the loudspeakercan be determined based on the estimated value of the diaphragm relativespeed, the input current, and a DC impedance of the loudspeaker obtainedat the present moment. In this way, in the diaphragm displacement modelin accordance with embodiments of the present invention, the number ofweight values is relatively small.

Referring now to FIG. 3, shown is a diagram of an exampleelectromagnetic and mechanical vibration model of a loudspeaker, inaccordance with embodiments of the present invention. The diaphragm ofthe loudspeaker may vibrate and produce sound under the driving of anelectromagnetic field that is generated by an electromagnetic coil. InFIG. 3, loop 1 is an equivalent circuit of a driving coil. Also, u_(in)is a driving voltage (e.g., an input voltage of the driving coil orvoice coil), R is a resistance of the driving coil (e.g., a DC impedanceof the loudspeaker), L is an inductance of the driving coil, l is atotal length of the driving coil, and B denotes the magnetic inductionintensity in the gap between a magnet of the driving coil and a magnetof the diaphragm. When the driving coil is not energized, the magnetinduction intensity in the magnetic pole gap between a permanent magnetof the driving coil and a permanent magnet of the diagram is asubstantially constant value. Also in FIG. 3, i is a current in the loop1 (e.g., a current flowing through the driving coil), and v is acoupling voltage at the driven side.

In FIG. 3, loop 2 is an equivalent model of a mechanical vibrationsystem coupling with the driving coil. Here, different parameters in themechanical mechanics system may be equivalent to one or more circuitcomponents. The electromagnetic induction force F can be generated byinduction voltage u_(in), and may be equivalent to the current in loop2. The quality of the mechanical vibration system, the force of thediaphragm, and the damping of the mechanical vibration system havedifferent properties for the applied force, and these may be equivalentto the parallel capacitance, inductance, and resistance.

Thus, the relationship between input current i, driving voltage u_(in),diaphragm speed v, and the diaphragm displacement s may satisfy theequations below:

$\quad\left\{ \begin{matrix}{{{Ri} + {L\frac{di}{dt}} + {Blv}} = u_{in}} \\{{{m\frac{dv}{dt}} + {R_{m}v} + {ks}} = {Bli}} \\{\frac{ds}{dt} = v}\end{matrix} \right.$

Here, m is the diaphragm quality of the loudspeaker, R_(m) is themechanical damping of the loudspeaker, and k is an elastic coefficientof the diaphragm. If the model of the above formula is directly used toestimate the diaphragm displacement, due to the number of parametersutilized, the computation can be relatively complex. In addition, BI maybe a nonlinear parameter of relatively poor stability, and its usage inmodeling an electric-mechanical system and a mechanical-sound system ofthe loudspeaker can result in further complexity.

Since the inductor can mainly respond to the high-frequency AC currentand the effect on driving voltage u_(in) can be neglected, the factorrelated to the inductor can be omitted in the model. Also, nonlinearparameter B1 can equal 1 through per-unit processing by neglecting itsnonlinear characteristic. Accordingly, the corresponding displacementcan be converted to a relative displacement parameter after thenonlinear portion of the model is neglected. Thus, the diaphragmdisplacement model of particular embodiments can be obtained as shownbelow:

$\quad\left\{ \begin{matrix}{{{R \cdot {i(k)}} + {v(k)}} = {u(k)}} \\{{v\left( {k + 1} \right)} = {{a \cdot {i(k)}} + {\left( {1 - b} \right) \cdot {v(k)}} + {c \cdot {s(k)}}}}\end{matrix} \right.$

Here, a, b and c are weight values of the model, and s(k) is thediaphragm relative displacement at the moment k. The model may be morestable when the coefficient of the diaphragm relative speed v(k) is 1−b.In the above formula, DC impedance R of the loudspeaker is apredetermined value, which can be obtained by any suitable approach,such as estimation. The DC impedance R in the model is a known value,and thus may not need to be obtained through an iteration of the model.In this way, only three weight values a, b, and c in the above formulamay be need updating in order to estimate the diaphragm relativedisplacement s.

In certain embodiments, the input current, the loudspeaker diaphragmrelative speed, and the relative displacement obtained by estimation canbe configured as inputs, and the driving voltage of the loudspeaker canbe configured as an output. Also, the three weight values of thedisplacement model can be adjusted through an adaptive filteringapproach, until the error e between the estimated value of drivingvoltage u_(e) and measured value u_(d) of the driving voltage converge(e.g., to be less than a predetermined threshold). In this way, thediaphragm displacement model corresponding to the current weight valuecan accurately simulate the state of the loudspeaker. Further, the modelmay be adapted to subsequent diaphragm displacement estimation. Thus inparticular embodiments, the state of the loudspeaker can be estimatedwhile on line or in operation.

Referring now to FIG. 4, shown is a flow diagram of an example method ofadjusting a weight value, in accordance with embodiments of the presentinvention. In this particular example, S100 of FIG. 1 can include, atS110, calculating diaphragm relative speed v(k+1) and diaphragm relativedisplacement s(k+1) at a next moment according to the diaphragmdisplacement model corresponding to weight values a(k), b(k) and c(k) atthe present moment. For example, according to the above formulas, S110can be executed according to the following formulas:

v(k+1)=a(k)*i(k)+(1−b(k))*v(k)+c(k)*s(k)

s(k+1)=ts*v(k)+s(k)

u(k)=v(k)+R*i(k)

Here, ts is a time length between two adjacent timings, u(k) is anestimated value of the driving voltage. At S120, the error can becalculated according to the estimated value of the driving voltage, andthe measured value of the driving voltage of the loudspeaker at thepresent moment. For example, the error can be obtained by calculatingthe difference of the estimated value and the measured value of thedriving voltage, as shown below:

e(k)=umeas(k)−u(k)

Here, e(k) is the error at the present moment, and umeas(k) is themeasured value of the driving voltage. At S130, if the error is greaterthan the predetermined threshold, the weight value can be updated basedon historical data of loudspeaker parameters through the adaptivefiltering method.

For example, the weight values can be updated by using any suitableadaptive filtering algorithm for system identification. In one example,a least mean square (LMS) algorithm may be applied to update the weightvalues. The LMS algorithm can minimize the mean square value of theerror between the output signal and the expected response of the filter.In the LMS algorithm, the weight vector may be defined as W(k)=[a(k),b(k), c(k)], and the iterative factors mua, mub and muc below can beselected to calculate the weight vector value for every time. Forexample, the weight vector can be updated with reference to thefollowing formulas:

sa(k)=ts*va(k−1)+sa(k−1);

va(k)=(1−b(k))*va(k−1)+c(k)*sa(k−1)+i(k);

ua(k)=va(k);

a(k+1)=a(k)+mua*e(k)*ua(k);

sb(k)=ts*vb(k−1)+sb(k−1);

vb(k)=(1−b(k))*vb(k−1)+c(k)*sb(k−1)−vest(k−1);

ub(k)=vb(k);

b(k+1)=b(k)+mub*e(k)*ub(k);

sc(k)=ts*vc(k−1)+sc(k−1);

vc(k)=(1−b(k))*vc(k−1)+c(k)*sc(k−1)+sest(k−1);

uc(k)=vc(k);

c(k+1)=c(k)+muc*e(k)*uc(k)

In the above formulas, sa, sb and sc are the gradient vectors of thediaphragm displacement to the weight vectors a, b and c, respectively.In addition, ua, ub and uc are the gradient vectors of the voltage tothe weight vectors a, b and c, respectively. Also, va, vb and vc are thegradient vectors of the diaphragm relative speed to the weight vectorsa, b and c, respectively.

After the execution of S130 is completed, the process can return to S110for iteration, until the error between the estimated value and themeasured value of the driving voltage satisfied the predeterminedthreshold value. Those skilled in the art will recognize that othertypes of adaptive filtering algorithms can alternatively be employed inorder to iterate and update the parameters of the model.

Referring back to FIG. 1, at S200, the diaphragm relative displacementof the loudspeaker can be estimated according to the diaphragmdisplacement model corresponding to the final determined weight values.The diaphragm displacement can be accurately estimated according to thedetermined diaphragm displacement model. In addition, since theparameters to be adjusted and updated are fewer as compared to otherapproaches, the construction process of the diaphragm displacement modelmay converge relatively quickly.

After the relative displacement is obtained, the corresponding controlcan be directly executed according to the relative displacement. In somecases, further estimation of the absolute displacement of the diaphragmmay be needed based on the relative displacement. In such cases, atS300, a diaphragm absolute displacement can be obtained based on apredetermined relationship between the diaphragm relative displacementand the diaphragm absolute displacement, and the diaphragm relativedisplacement may be obtained by calculation.

As mentioned above, B1 of the model can be 1 through per-unit process,and the system identification parameters may be reduced, so s(k) of themodel obtained through estimation may be the relative displacement, asopposed to the absolute displacement. Since the absolute displacement isrelated to the nonlinear parameter B1, it exhibits a strong nonlinearcharacteristic. In some cases, the diaphragm absolute displacement canbe measured, and the diaphragm relative displacement can be estimated atthe same time, and a corresponding relationship between them can be setup. At S300, on the basis of the such a relationship obtained inadvance, the corresponding diaphragm absolute displacement can beobtained according to the diaphragm relative displacement. For example,corresponding relationship can be embodied as a correspondingrelationship table, or a proportion function curve based oncorresponding relationship.

In particular embodiments, methods as described herein may be suitablefor application in loudspeaker driving circuits for estimating theloudspeaker diaphragm in real time, and can be adapted to or includedwithin digital integrated circuits for processing, and/or as programsexecuted by a general processor, due to attendant advantages of fastconvergence and high accuracy. In particular embodiments, an inputcurrent, a relative speed, and a relative displacement the loudspeakerdiaphragm (e.g., obtained through estimation) can be received as inputs,and a driving voltage of the loudspeaker can be provided as an output.

A non-linear motor coupling coefficient can be set to be 1 throughper-unit processing, and a more simplified loudspeaker diaphragmdisplacement model can be obtained. Also, the weight value of thediaphragm displacement model can be adjusted based on an adaptivefiltering method, until the error between the estimated value of thedriving voltage and the measured value of the driving voltage is lessthan a predetermined threshold. Further, the relative displacement ofthe diaphragm can be determined according to the finally determinedweight value, in order to quickly and accurately estimate theloudspeaker diaphragm displacement, and realize accurate control of theloudspeaker.

The embodiments were chosen and described in order to best explain theprinciples of the invention and its practical applications, to therebyenable others skilled in the art to best utilize the invention andvarious embodiments with modifications as are suited to particularuse(s) contemplated. It is intended that the scope of the invention bedefined by the claims appended hereto and their equivalents.

1. A loudspeaker diaphragm state estimation method, the methodcomprising: a) determining a weight value of a diaphragm displacementmodel to make an error between an estimated value of a driving voltageof a loudspeaker and a measured value of said driving voltage to be lessthan a predetermined threshold; b) estimating a diaphragm relativedisplacement of said loudspeaker according to said diaphragmdisplacement model that corresponds to said weight value; and c)configuring an input current, a diaphragm relative speed, and adiaphragm relative displacement as input signals, and said drivingvoltage as an output signal, in order to achieve said diaphragmdisplacement model.
 2. (canceled)
 3. The method of claim 1, wherein saiddiaphragm displacement model is: $\quad\left\{ \begin{matrix}{{{R \cdot {i(k)}} + {v(k)}} = {u(k)}} \\{{v\left( {k + 1} \right)} = {{a \cdot {i(k)}} + {\left( {1 - b} \right) \cdot {v(k)}} + {c \cdot {s(k)}}}}\end{matrix} \right.$ wherein R is said DC impedance of saidloudspeaker, i(k) is said input current at moment k, v(k) is saiddiaphragm speed at moment k, u(k) is said estimated value of saiddriving voltage at moment k, s(k) is said diaphragm relativedisplacement, and a, b and c are weight values corresponding to i(k),v(k) and s(k).
 4. The method of claim 1, wherein a motor couplingcoefficient is per-unit value normalized to 1 from a non-linear value.5. (canceled)
 6. The method of claim 1, further comprising determining adiaphragm absolute displacement in accordance with a predeterminedrelationship between said diaphragm relative displacement and saiddiaphragm absolute displacement, wherein said diaphragm relativedisplacement is obtained by calculation.
 7. The method of claim 6,wherein said predetermined relationship of said diaphragm relativedisplacement and said diaphragm absolute displacement is a proportionfactor that is measured in advance.
 8. A loudspeaker driving circuit,comprising a processor that is adapted to execute the method of claim 1.9. The method of claim 1, further comprising: a) determining a diaphragmrelative speed at a next moment in accordance with said input current, aproduct value of a vector determined by an estimated value of adiaphragm relative speed and an estimated value of a diaphragm relativedisplacement, and said weight value vector obtained at the presentmoment; and b) determining said estimated value of said driving voltagein accordance with said estimated value of said diaphragm relativespeed, said input current, and a DC impedance of said loudspeakerobtained at said present moment.
 10. The method of claim 1, wherein saidweight value is adjusted by an adaptive filtering method.
 11. The methodof claim 10, wherein a said adaptive filtering method comprises: a)determining said diaphragm relative speed and said diaphragm relativedisplacement at said next moment according to said diaphragmdisplacement model that corresponds to said weight value obtained atsaid present moment; b) determining said estimated value of said drivingvoltage at said present moment; c) determining said error according tosaid estimated value of said driving voltage and said measured value ofsaid driving voltage of said loudspeaker at said present moment; and d)updating said weight value based on historical data of loudspeakerparameters through said adaptive filtering when said error is largerthan said predetermined threshold.
 12. The method of claim 10, whereinsaid adaptive filtering method is a least mean square algorithm (LMS).13. The method of claim 12, wherein said DC impedance of saidloudspeaker is obtained by estimation.